This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this research is to refine and improve the methodology of flow and perfusion imaging (DTI) for the investigators and collaborators on the P41 RR09784 ?Center for Advanced MR Technology at Stanford? effort (Core3). The rationale for using perfusion MRI (PWI) is that the perfusion thresholds for functional deficits in ischemia are slightly above that for reductions in the apparent diffusion coefficient (ADC). Thus, if there is no DWI lesion, ischemia may still be the underlying cause of the patient?s symptoms, which can be revealed by PWI. In these patients (perfusion deficit, but no DWI abnormality), blood flow appears to be impaired, but not severely enough to cause energy failure in the affected region, suggesting that most or all of the affected tissue is still potentially salvageable. We hypothesize that measured perfusion (CBF, MTT, and CBV) values would reveal the irreversible tissue from the reversible events at presentation, subsequent measures will test this. We have used our refinements of the CBF mapping PWI methods developed here to study the clinical and radiological correlates of patients with a severe reduction of CBF using PWI with the CBF corrected by the Ostergaard CBF approach. We propose to further study this interesting ADC-CBV tissue pattern. These data suggest that severe CBF reductions of greater than 50% result in more severe cerebral ischemia, as measured by a higher NIHSS, a lower traceADC, a larger DWI lesion and a larger perfusion deficit. We now are attempting to ?titrate? the observed ADC decreases with measured CBF values acquired from the MRI and from XeCT studies on consecutive patients.